The present invention relates to heat-sensitive microcapsules that are broken by heating to a predetermined temperature, and recording mediums using the heat-sensitive microcapsules.
Recording mediums comprising a substrate such as a paper sheet coated with microcapsules containing a coloring composition have been well known. Known as an example thereof are photo-sensitive recording mediums using photo-sensitive microcapsules comprising a shell wall of a photosetting resin. The photo-sensitive recording mediums are exposed to light correspondingly to a desired image pattern and applied a predetermined pressure to, thereby recording images. Thus, the photo-sensitive microcapsules not exposed to light are broken and the microcapsules exposed to light, photo-set microcapsules, are not broken by the pressure, whereby on a layer of the microcapsules is recorded an image corresponding to the light exposure pattern.
However, the photo-sensitive recording mediums must be produced and stored in a light-screening environment to prevent the photo-sensitive microcapsules from photosetting. On the photo-sensitive recording mediums must be recorded images in such an environment. Further, because the photo-sensitive microcapsules not exposed to light are broken with ease, the photo-sensitive recording mediums comprising the photo-sensitive microcapsules must be handled without external force. Therefore, the photo-sensitive recording mediums are put in a light-screening package, etc. to store, thereby increasing costs and size of a recording device using the mediums. The light-screening package, etc. is disposed as a waste product.
Heat-sensitive recording mediums using heat-sensitive microcapsule that is broken by heating to a predetermined temperature are also known. The heat-sensitive microcapsule may contain a diazo compound, a colorless leuco-dye such as a fluoran compound, etc. as a color-producing agent. In the case of the heat-sensitive microcapsule containing the leuco-dye, the heat-sensitive microcapsule is heated to melt its shell wall or to make the leuco-dye permeate through the shell wall, whereby the leuco-dye comes into contact with a color-developing agent such as Bisphenol A to exhibit color. In the case of the heat-sensitive microcapsule containing the diazo compound, a coupler may be used instead of the color-developing agent. The heat-sensitive microcapsule may contain the color-developing agent or the coupler. The heat-sensitive microcapsule releases the color-developing agent or the coupler by heating to make it come in contact with the leuco-dye or the diazo compound. Thus, the color-producing agent is stably isolated from the color-developing agent or the coupler. Polyurea/polyurethane microcapsules, gelatin microcapsules, U/F (urea/formalin) microcapsules, M/F (melamine/formalin) microcapsules, etc. are known as such a heat-sensitive microcapsule.
With regard to the heat-sensitive recording medium mentioned above, the color-producing agent interacted with the color-developing agent or the coupler is generally fixed to the substrate by irradiating a particular light such as ultraviolet. The image-recording device using the heat-sensitive recording medium is required to have a light irradiation unit, thereby inevitably increasing power consumption. Further, in the case where a color image is recorded on the heat-sensitive recording medium, heating and light irradiation must be repeatedly carried out to every color, failing to rapidly form the color image. Furthermore, above-described heat-sensitive microcapsules are insufficient in heat-responsiveness so that the shell wall thereof is not sensitively melted. Thus, although the heat-sensitive microcapsules have known as a general idea, there is no example of the microcapsules that can be sensitively broken even by heating in a short time. Further, the reaction between the leuco-dye and the color-developing agent is reversible, whereby the heat-sensitive recording mediums using the leuco-dye are generally poor in stability of recorded image and reliability.
Accordingly, a first object of the present invention is to provide a first heat-sensitive microcapsule stable to light and easy to handle.
A second object of the present invention is to provide a second heat-sensitive microcapsule that is sensitively broken even by heating in a short time.
A third object of the present invention is to provide recording mediums comprising a heat-sensitive microcapsule, which provides substantially no waste products after recording, is easy to handle, and capable of economically recording an image with ease.
As a result of intense research in view of the first object, the inventors have found that a novel microcapsule comprising a liquid coloring composition, which is broken by its increased internal pressure provided by heating to a temperature equal to or higher than a boiling point of the liquid coloring composition, is stable to light and easy to handle. Thus, a first heat-sensitive microcapsule of the present invention comprises a shell wall and a liquid coloring composition enclosed in the shell wall, and has such a temperature-breaking characteristic that the shell wall is broken by heating to a temperature equal to or higher than a boiling point of the liquid coloring composition to release the liquid coloring composition. The first heat-sensitive microcapsule of the present invention is broken to release its enclosures not by melt of the shell wall, but by increased inner pressure provided by vaporization of the liquid coloring composition, being deferent from conventional heat-sensitive microcapsules.
As a result of intense research in view of the second object, the inventors have found that a heat-sensitive microcapsule containing at least a gas-developing agent and a coloring composition is sensitively broken even by heating in a short time. Thus, a second heat-sensitive microcapsule of the present invention comprises a shell wall, and a coloring composition and a heat decomposition-type gas-developing agent enclosed in the shell wall, and has such a temperature-breaking characteristic that the shell wall is broken by heating to a temperature equal to or higher than a decomposition temperature of the heat decomposition-type gas-developing agent to release the coloring composition. In the second heat-sensitive microcapsule of the present invention, the gas-developing agent is decomposed at a temperature equal to or higher than its decomposition temperature to provide N2 gas, etc., thereby increasing the inner pressure of the microcapsule. Therefore, the shell wall of the microcapsule is sensitively broken by the increased inner pressure to fix the coloring composition to the substrate. The second heat-sensitive microcapsule of the present invention is broken to release its enclosures not by melt of the shell wall, but by increased inner pressure provided by decomposition of the gas-developing agent, being deferent from conventional heat-sensitive microcapsules.
A first recording medium of the present invention is a heat-sensitive recording medium comprising a substrate coated with a microcapsule layer including the first heat-sensitive microcapsule. The first recording medium is capable of economically recording a single color image with ease.
A second recording medium of the present invention is a heat-sensitive recording medium comprising a substrate coated with a microcapsule layer including the second heat-sensitive microcapsule. The second recording medium is capable of economically recording a single color image with ease.
A third recording medium of the present invention is a pressure-sensitive, heat-sensitive recording medium comprising a substrate coated with a microcapsule layer. The microcapsule layer comprises upper, middle and lower portions, the lower portion being disposed on the substrate, the middle portion being disposed on the lower portion, the upper portion being disposed on the middle portion. The upper portion includes a plurality of first pressure-sensitive microcapsules uniformly distributed in a first binder having a predetermined melting temperature, the first pressure-sensitive microcapsules each containing a first coloring composition. The middle portion includes a plurality of second pressure-sensitive microcapsules uniformly distributed in a second binder having a melting temperature higher than the melting temperature of the first binder, the second pressure-sensitive microcapsules each containing a second coloring composition. The lower portion includes a plurality of third pressure-sensitive microcapsules and a plurality of heat-sensitive microcapsules uniformly distributed in a third binder having a melting temperature higher than the melting temperature of the second binder, the third pressure-sensitive microcapsules each containing a third coloring composition, the heat-sensitive microcapsules each containing a fourth coloring composition. The first pressure-sensitive microcapsule is broken under a first pressure at a first temperature higher than the melting temperature of the first binder, the second pressure-sensitive microcapsule is broken under a second pressure lower than the first pressure at a second temperature higher than the melting temperature of the second binder, the third pressure-sensitive microcapsule is broken under a third pressure lower than the second pressure at a third temperature higher than the melting temperature of the third binder, and the heat-sensitive microcapsule has such a temperature-breaking characteristic that the heat-sensitive microcapsule is broken by heating to a fourth temperature higher than the third temperature to release the fourth coloring composition. As the heat-sensitive microcapsule, the first or second heat-sensitive microcapsule of the present invention may be preferably used. The third recording medium is capable of economically recording a color image with ease.
A fourth recording medium of the present invention is a pressure-sensitive, heat-sensitive recording medium comprising a substrate coated with a microcapsule layer. The microcapsule layer comprises upper and lower portions, the lower portion being disposed on the substrate, the upper portion being disposed on the lower portion. The upper portion includes a plurality of first pressure-sensitive microcapsules uniformly distributed in a first binder having a predetermined melting temperature, the first pressure-sensitive microcapsules each containing a first coloring composition. The lower portion includes a plurality of second pressure-sensitive microcapsules and a plurality of heat-sensitive microcapsules uniformly distributed in a second binder having a melting temperature higher than the melting temperature of the first binder, the second pressure-sensitive microcapsules each containing a second coloring composition, the heat-sensitive microcapsules each containing a third coloring composition. The first pressure-sensitive microcapsule is broken under a first pressure at a first temperature higher than the melting temperature of the first binder, the second pressure-sensitive microcapsule is broken under a second pressure lower than the first pressure at a second temperature higher than the melting temperature of the second binder, and the heat-sensitive microcapsule has such a temperature-breaking characteristic that the heat-sensitive microcapsule is broken by heating to a third temperature higher than the second temperature to release the third coloring composition. As the heat-sensitive microcapsule, the first or second heat-sensitive microcapsule of the present invention may be preferably used. The fourth recording medium is capable of economically recording a color image with ease.
A fifth recording medium of the present invention is a pressure-sensitive, heat-sensitive recording medium comprising a substrate coated with a microcapsule layer. The microcapsule layer includes a plurality of pressure-sensitive microcapsules and a plurality of heat-sensitive microcapsules uniformly distributed in a binder having a predetermined melting temperature, the pressure-sensitive microcapsules each containing a first coloring composition, the heat-sensitive microcapsules each containing a second coloring composition. The pressure-sensitive microcapsule is broken under a predetermined pressure at a first temperature higher than the melting temperature of the binder, and the heat-sensitive microcapsule has such a temperature-breaking characteristic that the heat-sensitive microcapsule is broken by heating to a second temperature higher than the first temperature to release the second coloring composition. As the heat-sensitive microcapsule, the first or second heat-sensitive microcapsule of the present invention may be preferably used. The fifth recording medium is capable of economically recording a color image with ease.
A sixth recording medium of the present invention is a pressure-sensitive, heat-sensitive recording medium comprising a substrate coated with a microcapsule layer. The microcapsule layer includes a plurality of first pressure-sensitive microcapsules, a plurality of second pressure-sensitive microcapsules and a plurality of heat-sensitive microcapsules uniformly distributed in a binder having a predetermined melting temperature, the first pressure-sensitive microcapsules each containing a first coloring composition, the second pressure-sensitive microcapsules each containing a second coloring composition, the heat-sensitive microcapsules each containing a third coloring composition. The first pressure-sensitive microcapsule is broken under a first pressure at a first temperature higher than the melting temperature of the binder, the second pressure-sensitive microcapsule is broken under a second pressure lower than the first pressure at a second temperature higher than the first temperature, and the heat-sensitive microcapsule has such a temperature-breaking characteristic that the heat-sensitive microcapsule is broken by heating to a third temperature higher than the second temperature to release the third coloring composition. As the heat-sensitive microcapsule, the first or second heat-sensitive microcapsule of the present invention may be preferably used. The sixth recording medium is capable of economically recording a color image with ease.